Hitachi VT-6500A Audio Playback

[ThePlague]

Originally Posted by Electronic M

I don't think that's your problem.

The audio recording bias Oscillator is only supposed to run while recording. That osc runs at above audible frequencies to facilitate correctly magnetizing the tape during recording...If you run the record osc during playback it may damage the existing recording.

If you can identify the audio playback head (its often clustered with the tracking control track head) you could try injecting low-level audio there and see if it makes it through.
Some decks especially mid-80's and older had long multi-pole switches on the PCBs that look like those found in 70's and 80's cassette decks. Those PCB switches have to connect into the mechanism correctly to play properly....Case in point I worked on a sony SL-5800 Beta deck where the bottom PCB had such switches and if the bottom PBC was hinged down into service mode (which I needed to do) the switch on the PCB that switched audio from tuner to tape would not be engaged by the mech and stay in tuner mode (I could manually toggle it).

Not familiar with your model so I can't offer much more insight.

No large multi-pole switches on this unfortunately. All soft touch logic. As much as I enjoy this portable systems, the weird design choices made to build to a size always incur the strangest servicing quirks. I will go ahead and try and see if there is an audio signal coming off of the audio playback head to verify the audio board is actually getting a signal.

Originally Posted by JohnCT

I never say never as I've seen stuff in my 50 years in this business that would appear to make no sense.

Most of the time, a bad counter belt would cause (other than no counter movement) a shutdown in a few seconds as most of the counters had a hall effect sensor to inform the micro of tape movement, but of course, not all did.

Now, that machine looks suspiciously like the RCA convertible VFP series. We did have an audio problem with the RCA convertibles, and there are two tiny relays that can cause either noisy audio or no audio. I think they were identified as R400 or R1400 or so - maybe R1400 and R1401. See if there's any on the board marked something like that.

If that's your problem, there's a *small* chance I may have a couple in an RCA box.


John

This unit seems to have the hall effect sensor on the pulley attached to the take up reel instead of on the counter side pulley itself. Lets the unit play without having a working counter I suppose.

Looking at the audio board in the unit and the schematic, it would seem that you are correct. There are two small relays labeled RL402 and RL401. I am not sure if these would produce an audible click, but I do not here any actuation noise. When I get the chance I will try and test these out.

If you do happen to have a couple, I would be more than happy to pay you for them. Even if it isn't the issue, it would be nice to have a spare set.